Inflammatory response, tissue repair and regeneration, cancer, arthritis, atherosclerosis, and congenital brain defects. Understanding cell migration is challenging, since it requires understanding both the mechanisms that drive and regulate its component processes, e.g., front-back polarization, protrusion, and the formation and disassembly of adhesions, and the mechanisms that integrated them spatially and temporally. This renewal builds on the significant progress that we have made over the past 4 years; they include new imaging modalities for mapping molecular interactions and dynamics at high spatial resolution, identification of a new class of adhesions, nascent adhesions, that drive migration by signaling to Rac near the leading edge, demonstration that myosin II polarizes the cell and regulates and spatially integrates the component processes that comprise cell migration, visualization of adhesions in 3-dimensional matrices, and the demonstration that dendritic spine dynamics and post synaptic density organization are highly analogous to adhesion and protrusion in migrating cells. In this renewal, we develop these insights and bring state of the art imaging methods for identifying protein complexes to understand the nucleation and early events in adhesion assembly, determine when, where, and how adhesions generate migration-related signals and what regulates them, determine how myosin II generates front-back polarity and contact inhibition of migration, and how myosin II mediates mechanotransduction by interpreting and integrating extracellular pliability. We translate these observations to migration in 3-dimensions and to dendritic spine morphology and post synaptic density organization in hippocampal neurons. We will study neuronal and fibroblastic cells using a prioritized list of signaling and structural molecules. The proposed studies bear directly on tumor cell invasion, chronic inflammation, mental retardation, schizophrenia, and regenerative therapies using stem cell transplantation.